Chapter 20 EXAM @ Flashcards
Define the cardiac cycle.
Period of time fr start of 1 heart beat to the start of next
Cardiac muscle tissue contracts on its own without neural or hormonal stimulation b/c of a phenomenon known as what?
Automaticity
What are the 3 components of the cardiac conducting system?
Sinoatrial Node
Atrioventricular node
Conducting cells
The SA node is located where?
Posterior wall of the R atrium nr entrance of the superior venacava
What is the location of the atrioventricular node?
Within the fl of the R atrium nr the opening of the coronary sinus
What pathways does a contractile stimulus follow to atrial muscle cells as an electrical impulse travels fr the SA node to the AV?
Internodal pathways
Which conducting cells are located in the ventricles?
AV bundle (bundle of his)
Bundle branches
Purkinje fibers
The gradual depolarization of the conducting cells of the SA node and the AV node is known as ___.
Prepotential
What causes pre potential of cardiac cells?
Slow influx of Na+ w/o a compensating outflow of K+
The ___ node generates action potentials at a rate of 80-100 per minute
SA
The AV node generates action potentials at what rate?
40-60/min
The SA node contains ___ ___ which set the heart rate.
Pacemaker cells
What connects the SA node to the AV node?
Internodal pathways
The connection between the AV node and the ___ ___ (aka ___ of ___), is normally the only elec connection between the atria and the ventricles.
AV Bundle
Bundle of his
Once an impulse enters the AV bundle, it travels to the interventricular septum and enters what part of the conduction sys?
Right and left bundle branches
What is an ectopic pacemaker?
Cells outside the conduction sys that set the HR that disrupt the the timing of the ventricular contraction
Which wave on the EKG represents the atrial depolarization?
P wave
The smaller ___ wave indicates ventricular depolarization.
T
The ___ interval extends fr the start of atrial depolarization to the start of the QRS complex
P-R
Extension of the P-R interval to longer than ____ can indicate damage to the conducting pathways or the AV node.
200 msec
The Q-T interval indicates what?
Time required for the ventricles to undergo a single cycle of depolarization and repolarization
What are some of the causes of long QT syndrome?
Electrolyte disturbances Meds Conduction probs Coronary ischemia Myocardial damage
An ____ is an irregularity in the normal rhythm or force of the heartbeat.
Arrhythmia
Serious arrhythmias may indicate what issues?
Damage to myocardium
Injuries to pacemakers or conduction pathways
Exposure to drugs
Abnormalities in electrolyte composition of
extracellular fluids
What is the resting potential of a ventricular contractile cell?
-90mV
An action potential begins when the membrane of ventricular muscle reaches threshold at approx ____ mV.
-75 mV
What are the 3 steps in an action potential?
- Rapid Depolarization
- The Plateau
- Repolarization
Fast sodium channels open during the rapid depolarization phase of an action potential. They are called fast channels b/c . . . .
They open quickly & remain open only for a few milliseconds
At what point in the action potential of a cardiac cell do sodium channels close?
As transmembrane potential reaches +30mV
Voltage gated Ca+ channels are known as slow Ca+ channels. Why?
B/c they open slowly & remain open for for a relatively long period
What causes the rapid depolarization phase of an action potential?
Na+ entry
How long does the rapid depolarization phase of an action potential last?
3-5 msec
What is the last thing that happens during the depolarization phase of the action potential?
Closure of voltage gated fast sodium channels
The plateau phase of the action potential begins with what?
Ca2+ entry
The plateau phase of the action potential lasts how long?
-175 msec
The plateau phase of the action potential ends with the closure of ___ ___ ___.
Slow calcium channels
What causes the repolarization phase of the action potential to start?
Loss of K+
What is the duration of the repolarization phase of an action potential?
75 msec
The repolarization phase of the action potential ends with what?
Closure of slow K channels
The period when a membrane will not respond to another stimulus for sometime after and action potential begins is know as what?
Refractory Period
What is the approx length of the refractory period in ventricular muscle?
200 msec
Define cardiac cycle.
The period between the start of one heart beat & the beginning of the next
What are the 2 phases of the cardiac?
Systole and Diastole
The phase in the cardiac cycle when a chamber contracts and pushes blood is known as what?
Systole
The phase in the cardiac cycle when the muscle relaxes and the chambers fill is known as ___.
Diastole
The brief period when all heart valves are closed, volumes in the ventricles do not change and ventricular pressures are rising is known as ___ ___.
Isovolumetric Contraction
What IDs the beginning point of ventricular ejection?
When pressure in ventricles exceeds that in arterial trunks, semilunar valves open and blood flows
During ventricular ejection each ventricle ejects 70-80 mL of blood. This is known as what?
Stroke volume
The amt of blood remaining in the ventricle when the semilunar valve closes is known as what?
End-systolic volume
The period when heart valves are closed, ventricular myocardium is relaxing and ventricular pressures are still higher than atrial pressures is known as what?
Isovolumetric relaxation
What happens to ventricular pressure during isovolumetric relaxation?
Ventricular pressure drops rapidly
Heart sound S1 marks what in the cardiac cycle?
Start of ventricular contraction when the AV valves close
When does the heart sound S2 occur?
At beginning of ventricular filling when semilunar valves close
What is occurring during heart sound S3?
Blood is flowing into the ventricles
What is occurring during heart sound S4?
Atrial contraction
What causes a heart murmur?
Probs w/papillary muscles or chordae tendineae causing heart valves to not close properly causing AV valve regurgitation
What is the term used to refer to the movements and forces generated during cardiac contractions?
Cardiodynamics
The amt of blood left in the ventricles at the end of ventricular diastole is called what?
End Diastolic Volume
The amt of blood left in the ventricles at the end of ventricular systole is called ___ -___ volume.
End-systolic
What is stroke volume?
Amt of blood pumped out of each ventricle during a single beat
What is the equation for Stroke Volume?
SV = End diastolic vol - End Systolic vol
The percentage of the End diastolic col represented by the Stroke Vol is called ___ ___.
Ejection Fraction
Define cardiac output.
Amt of blood pumped out of the L ventricle in one minute
What equation can we use to determine cardiac output?
CO = HR x SV
What are 2 factors affecting HR?
Autonomic Innervation
Hormones
What are 2 factors affecting stroke vol?
End diastolic vol
End systolic vol
The ANS and PNS innervate the heart by means of the nerve network known as the ___ ___.
Cardiac plexus
What is the location of the autonomic HQ for cardiac control?
Cardiac centers of the medulla oblongata
The ____ center controls sympathetic neurons that increase HR.
Cardioacceleratory
The ____ center controls parasympathetic neurons that slow HR.
Cardioinhibitory
Where do the cardioacceleratory and cardioinhibitory centers receive their info from?
Reflex pathways
Higher centers
PNS & SNS ctrs in Hypothalamus
Cardiac centers monitor baroreceptors and chemoreceptors innervated by what 2 nerves?
Glossopharyngeal (CN IX)
Vagus (CN X)
Cardiac centers respond to changes in ___ ___ reported by baroreceptors and to what 2 things from chemoreceptors?
Blood Pressure
Changes in arterial concentrations of dissolved O2 and CO2
What are 2 ways to increase HR through ANS innervation?
Decrease PNS activity
Increase SNS activity
How do SNS and PNS alter HR?
By changing ionic permeabilities of cells in the conducting sys.
Adjustments in HR in response to increases in venous return are caused by what reflex?
Arterial reflex of Bainbridge principle
What is the term given to the amt of blood returning to the heart by the veins?
Venous return
___, ___ and thyroid hormone increase HR by their effect on the SA node.
Epi
Norepi
____ ___ is the duration of ventricular diastole and is dependent upon what?
Filling time
HR
The degree of stretching in ventricular muscle cells during ventricular diastole is called ____.
Preload
Preload is directly proportional to what?
EDV
The idea that increasing EDV results in a corresponding increase in stroke vol is know as ___-___ principle.
Frank-Starling
___is the amt of force produced during a contraction at a given preload.
Contractility
Inotropy is a term that is related to what with regards to the heart?
Force of contraction (contractility)
SNS stimulation has a ____ inotropic effect where as PNS stimulation has a ____ inotropic effect.
Positive
Negative
The ___ is the amount of tension that the contracting ventricle must produce to force open the semilunar valve and eject blood.
Afterload
As afterload ____ stroke volume ____.
Increases
Decreases
An increase in venous return stretches nodal cells and produces what effect?
Increases HR
Stroke vol is the difference between what and what?
EDV and ESV
What 3 factors effect ESV?
Preload
Degree of contractility
Afterload
The difference between resting and maximal cardiac output is known as ___ ___.
Cardiac reserve